If winds weaken, that gas and other volcanic pollutants can settle easily with moisture and dust to create a haze called volcanic smog, or “vog,” with tiny sulfuric acid droplets that can pose respiratory problems, according to the US Geological Survey.

Trade winds could weaken Thursday and Friday, meaning the vog that’s largely been accumulating over the ocean south of the Big Island could pool over a larger portion of it, creating possible health hazards, the National Weather Service says.

And with high chances of rain on those days, sulfuric acid droplets would fall, creating another menace known as acid rain, CNN meteorologist Michael Guy says.

Respiratory problems

At higher concentrations, vog can cause headaches and irritation to the lungs and eyes, the University of Hawaii at Hilo says.

“Because of their small size, aerosol particles such as those in vog penetrate deep into the human lung and are readily retained,” the USGS says.

High levels of acidic particles in vog “can induce asthma attacks, especially in adolescents, and can also impede the ability of the upper respiratory tract to remove other potentially harmful particles,” it says.

For people with asthma and other respiratory problems, “the effects are much more serious, causing a tightening of the airways in the lungs and making it very difficult to breathe,” the university says.

But it adds: “There’s been no clear evidence that vog causes lingering damage to normally healthy individuals.”

If trade winds become lighter as predicted later this week, vog could pool northward over parts of the island by Friday, the weather service says.

But winds are forecast to return — and the vog could be pushed off much of the island — by Friday night, it says.

What are the effects of acid rain? The droplets of sulfuric acid in vog have the corrosive properties of diluted battery acid, the USGS says.

“When atmospheric moisture is abundant, these droplets combine with it and fall as acid rain, damaging plants and accelerating the rusting of metal objects such as cars, industrial and farm equipment, and building components,” it says.

The amount of acid rain depends on the concentration of sulfur dioxide in the air, CNN’s Guy says.

Determining how acid rain affects human health is complicated, andGuy says the effects on the skin are unclear.

One direct, immediate threat is not the rain, but rather breathing in the particles in the vog — the very pollutants that caused the acid rain, according to the Environmental Protection Agency.

“Walking in acid rain, or even swimming in a lake affected by acid rain, is no more dangerous to humans than walking in normal rain or swimming in non-acidic lakes,” the EPA says.

That includes rooftop rainwater-catchment systems that Hawaii residents use for drinking water.

“In 1988, the drinking water of nearly 40% of homes using such systems in the Kona Districts of the island was found to be contaminated with lead leached by acid rain,” the USGS says. “Tests confirmed that the blood of some residents of these homes had elevated lead levels.”

Businger told Hawaii News Now that acid rain is not an immediate health hazard, adding that it’s “the least of their (residents) worries.”

More vents

Other dangers persist, not only in the form of lava but also earthquakes and newly formed cracks.

Two additional volcanic vents — the 13th and 14th — erupted Tuesday in the Leilani Estates area, where roughly 1,700 residents were asked to evacuate last week. At least 36 structures — including at least 26 homes — have been destroyed.

Residents are allowed to check on their properties from 7 a.m. to 6 p.m. each day but must be prepared to leave at a moment’s notice, the Hawaii County Civil Defense Agency says.